Earth tunnelling machines presently in use employ a toothed cutting head rotatably mounted on the end of a cylindrical housing. As the cutting head rotates and advances, the teeth on the head loosen the soil which passes through apertures in the head into the housing where it is collected and conveyed rearwardly. An example of such a head is disclosed in U.S. Pat. No. 3,961,825 issued June 8, 1976 to Lovat (the present inventor). In that particular apparatus movable doors are provided to control the entry of loose or soft soil through the cutting head into the housing and onto a conveyor, to prevent flooding. Full closure of the flood doors is made when loose or soft soil is being penetrated and the rotation of the cutting head has been stopped to advance and relocate the pushing rings at that end of the housing remote from the cutting head. Also in loose or soft soil it is desirable to close the flood doors where the apparatus is idle for a period of time, for example overnight, because when exposed to air the soil may increase in volume and flood the housing.
The problem with such a machine is that an excess of soil entering the machine in relation to the speed of advancement of the machine may cause the face of the tunnel to collapse if the soil at the face is loose and the flood gates do not react to the pressure change. Furthermore the pressure of the soil on the doors is perpendicular to their plane of movement to open and close.
It is an object of the invention to provide an improved tunnelling apparatus having a housing carrying a cutting head sealable from the housing.
It is another object of this invention to provide an improved cutting head for a tunnelling apparatus in which the soil transfer is controllable in response to earth pressure within the head.